Novel tetranuclear methine dyes, processes for preparing the same, and electrophotographic systems and silver halide emulsions containing the same

ABSTRACT

Novel tetranuclear dyes useful as sensitizers in electrophotographic systems as well as silver halide emulsions comprise compounds of the formula: Wherein A is selected from the group consisting of   R is alkyl; R1, R2 and R4 are selected from the group consisting of alkyl and carboxyalkyl; R3 is selected from the group consisting of hydrogen, alkyl and alkoxy; and Y is selected from the group consisting of Se and S; such compounds being characterized that when A is (1), B is (1); when A is (2), B is (2) and when A is (3), B is (4). Processes of producing such dyes as well as electrophotographic processes and materials containing the same are provided.

United States Patent Yao [451 Aug. 29, 1972 [54] NOVEL TETRANUCLEAR METI-IINE DYES, PROCESSES FOR PREPARING THE SAME, AND ELECTROPHOTOGRAPHIC SYSTEMS AND SILVER HALIDE EMULSIONS CONTAINING THE SAME [72] Inventor: Shi-Kuang Yao, Binghamton, NY.

13903 I [73] Assignee: GA F Corporation, New York, NY.

22 Filed: May 13,1968

21 Appl.No.: 728,837

[52] U.S. Cl. ..260/240.1, 96/ 1.6,96/ 1.7, 96/128, 260/2402 [51] Int. Cl. ..C09b 23/00 [58] Field of Search ..260/240.1, 240.2

[56] References Cited UNITED STATES PATENTS 3,379,533 4/ 1968 Jenkins et a1. ..260/240.2 X

2,518,731 8/ 1950 Thompson; ..260/240.l

3,152,905 10/1964 Gaspar ..260/240.1 X

FOREIGN PATENTS OR APPLICATIONS 540,578 10/ 1941 Great Britain ..260/240.1

Primary ExaminerJohn D. Randolph Attomey-Ge0rge L. Tone, Samson B. Leavitt and Walter C. Kehm ABSTRACT Novel tetranuclear dyes useful as sensitizers in electrophotographic systems as well as silver halide emulsions comprise compounds of the formula:

r s on s m 1 L 01 1 A 0 1; N N i, 1&1

Wherein A is selected from the group consisting of N 1'12 and B is selected from the group consisting of (l), (2) and (4) O N (lJ-C R:

l H R2 1? Ris alkyl;

R R and R are selected from the group consisting ofalkyl and carboxyalkgll; R is selected from e group consisting of hydrogen, alkyl and alkoxy; and Y is selected from the group consisting of Se and S; such compounds being characterized that when A is (1), B is (1); when A is (2), B is (2) and when A is (3), B is (4).

Processes of producing such dyes as well as electrophotographic processes and materials containing the same are provided.

6 Claims, No Drawings The present invention relates to novel tetranuclear methine dyes and methods of preparing the same as well as electrophotographic systems and silver halide emulsions containing such tetranuclear dyes as dyestuff l0 sensitizers.

It has now been discovered in accordance with the present invention that certain novel tetranuclear dyes possess excellent properties as dyestuff sensitizers both in electrophotographic processes and compositions as well as silver halide emulsions.

Thus, in accordance with the present invention, it has been discovered that certain novel methine tetranuclear dyes are capable of sensitizing the photoconductive insulating layer of both liquid toning and dry toning electrophotographic systems so as to increase the sensitivity of such layer by at least 50% while eliminating the effect of background bleaching or fading upon prolonged exposures associated with the use and B is selected from the group consisting of (l), (2)

and (4 S i l N R is alkyl;

R R and R are selected from the group consisting of alkyl and carboxyalkyl;

R is selected from the group consisting of hydrogen,

alkyl and alkoxy; and

Y is selected from the group consisting of Se and S;

such compounds being characterized that when A is (l), B is (1); when A is (2), B is (2) and when A is (3), B is (4).

Suitable alkyl radicals generally include those having from about one to about 20 carbon atoms, the lower alkyl radicals of from one to six carbon atoms being preferred. Representative alkyl groups include for exof conventional dyestuff sensitizers generally employed ample:

in electrophotographic processes and products.

Therefore, it is a principal object of the present invention to provide novel tetranuclear methine dyes and processes of producing the same.

It is a further object of the present invention to provide such a tetranuclear dyes wherein such dyes are useful as dyestuff sensitizers for photoconductive materials employed in electrophotographic and in photographic silver halide emulsion.

It is yet a further object of the present invention to provide electrophotographic systems including processes of electrophotographic reproduction and materials employed therein wherein the novel tetranuclear methine dyes of the present invention are utilized as dyestuff sensitizers effecting a greater than 50 percent sensitizing of the photoconductive material with an elimination of the effect of background bleaching or fading associated with conventionally employed materials. r

Still further objects and advantages of the compounds, compositions and processes of the present invention will become more apparent from the following more detailed description thereof.

The novel tetranuclear dyes of the present invention correspond to the general formula:

scH s l 0 l l o B A N N I R R1 Wherein A is sele cted from the group consisting of methyl ethyl n-vpropyl iso-propyl n-butyl t-butyl n-amyl iso-amyl n-hexyl n-heptyl 1 -methylhexyl n-octyl iso-octyl n-dodecyl n-tetradecyl n-hexadecyl n-octadecyl eicosyl etc.

Similarly, suitable carboxy alkyl radicals which can be employed in accordance with the present invention are those which contain from one to about 20 carbon atoms in the alkyl chain. Again, the carboxy lower alkyl group containing from one to about six carbon atoms in the lower alkyl chain are preferred. Illustrative carboxy alkyl groups employed in accordance with the present invention include:

carboxy methyl carboxy ethyl carboxy propyl carboxy butyl carboxy hexyl carboxy octyl carboxy dodecyl carboxy hexadecyl carboxy octadecyl etc.

In addition, suitable alkoxy substituents are those which contain from one to about six carbon atoms, i.e., lower alkoxy. Representative examples of such alkoxy substitutents include:

methoxy by reacting a di-quaternated salt of the general formula:

s :=orro-s 11+ l J 9 (iii I LII;S \N r -solh l t l h With a compound select d from the formulae:

R3 CH3 I J S=\N --0 1'1.

to yield compounds of the formulae:

/Y\ S-CH([3-S 1 /Y R3 /CCH iNJ O e O C\NLCH-C\ \ITI 1 1 11 l R2 R2 SCH(TS H+ s [o 9 OJ: s I D 1 l s 0 R R1 o N =s Generally, such a process is carried out by reacting approximately 2 moles of compound (A) or 2 moles of compound (B) per mole of the di-quaternated salt in order to produce the novel tetranuclear dye. The employment of greater amounts of compound (A) or compound (B) in the reaction with the di-quaternated salt, however, will not detract from the yield or purity of the desired tetranuclear dye but will only necessitate the removal of the excess reactant after completion of the reaction.

The temperature employed in the reaction in the production of the novel tetranuclear dyes in accordance with the present invention is in no way critical, the reaction preceding successfully from tempera tures ranging from ambient temperatures to highly elevated temperatures. Generally, however, temperatures within the range of 20 to 135C are preferred. Similarly, the pressure employed in the reaction of the present invention is in no way critical, and pressures ranging from sub-atmospheric pressure to highly elevated super-atmospheric pressures can be utilized.

The di-quaternated salts employed as a reactant in accordance with the process of the present invention in the production of the tetranuclear dyes are more fully described in co-pending application, Ser. No. 717896, filed 4/1/68 Thus, as disclosed in such co-pending application, the initial reactant is accordance with the process of the present invention comprises the unisolated intermediates produced from the quaternization of oxonols with transformation of the quaternary slats in aqueous alcohol or polar solvents to produce the diquaternated salts corresponding to the general formula:

with a trinuclear compound of the formula:

s CH(HJ|S G d L such compounds being reacted in substantially equimolar amounts so as to produce the desired tetranuclear dye. The trinuclear compounds which are employed as reactants in accordance with this embodiment to the present invention wherein unsymmetrical tetranuclear dyes are produced are the subject of applicants co-pending application, Ser. No. 717,896, which application more fully discloses the preparation of such trinuclear compounds. Accordingly, the subject matter of applicants co-pending application is herewith incorporated by reference as illustrating the preparation of the trinuclear reactant employed in the production of the production of the tetranuclear dyes of the present invention.

Exemplary tetranuclear dyes falling within the general formula above include, for example:

As indicated previously, the tetranuclear dyes of the t 35 lens-projected image or by contact-printing techniques,

present invention have found particular utility as sensitizers in electrophotographic systems as well as silver halide emulsions.

The novel tetranuclear dyes of the present invention are generally employed in electrophotographic layers and electrophotographic processes in which an electrostatic latent image is produced by utilizing the property of photoconduction (i.e., a variable conductivity dependent on the intensity of illumination). Such an electrophotographic reproduction process generally comprises one wherein a supported electrostatically charged photoconductive insulating layer is exposed and the resulting image subsequently developed with an electroscopic material. The improvement associated with such process is employing the novel tetranuclear dyes of the present invention as dyestuff sensitizers within the photoconductive insulating layer. Generally, the novel tetranuclear dyes are employed in an amount of from about 0.01 percent to about 5 percent by weight based on the photoconductive insulating layer, although slightly lower or greater amounts can be advantageously employed where desired for particular purposes. Thus, in such an electrophotographic process, the tetranuclear dyes of the present invention are employed as dyestuff sensitizers within a photoconductive insulating layer supported on a conductive support in the copy sheet, plate, or similar electrophotographic element.

The electrostatic latent image produced in the electrophotographic process may be produced in a conventional exposure operation, for example, by means of a whereby a non-visible electrostatic charge pattern (the so-called electrostatic latent image) is created on a surface in which pattern the charge density at any point is related to the intensity of illumination obtaining at that point during the exposure. The latent image may be developedi.e. rendered visible by means of an electroscopic powder, such as a color synthetic resin powder, and the resulting visible image may be fixed by rendering the powder permanently adherent to a support on which the image is desired, for example in suitable cases by heating to soften or melt the powder particles and/or the surface of the image support, or by application of an electric field, or with volatile solvents.

As noted above, in electrophotographic processes, such as embodied by the present invention, the electrostatic latent image is commonly formed on the surface of a photo-conductive insulating layer carried on a support. For example, material comprising such support and photoconductive layer may be sensitized by applying a uniform surface charge to the free surface of the photoconductive layer, for example, by means of a corona discharge, which charge is retained owing to the substantial insulating character, i.e. the low conductivity, of the layer in the dark. On exposure as described above, the photoconductive property of the layer causes the conductivity to increase in the illuminated areas to an extent dependent on the intensity of illumination, whereby the surface charge in the illuminated areas leaks away, leaving the charge located in the unilluminated areas, thus constituting the aforementioned charge pattern or electrostatic latent image. The electrostatic latent image can be developed (i.e.

rendered visible) by means of an electroscopic powder which adheres to the charged areas, particularly if the powder carries a charge of opposite polarity to that of the charge on the photoconductive material. Such opposite charge may be obtained by using the powder in admixture with a carrier such that the powder becomes suitably charged triboelectrically. A suitable developer may consist of a toner, such as a pigmented resin, and a carrier such as glass beads, and the powder image produced may be rendered permanent (fixed) by, for example, softening such resin toner by heat so that it adheres to a support carrying the powder imagewhich may be the original photoconductive material, or a separate support towhich the powder image can have been transferred. Liquid as well as powdered toner systems are applicable. 7

Materials generally known for the preparation of photoconductive insulating layers employed in electrophotographic reproduction processes include, for example, selenium, sulfur, zinc oxide and organic substances such as anthracene or anthraquinone. In addition, in recent years various organic heterocyclic materials have been developed which possess the property of acting as photoconductive materials employed in the photoconductive insulating layers utilized in electrophotographic processes. Thus, for example, some of these newly developed, heterocyclic materials include aryl furans, aryl thiophenes and aryl pyrroles such as shown in US. Pat. No. 3,174,854, N-disubstituted benzylideneazines as shown in U.S. Pat. No. 3 ,290, l 47, 2,5-bis (para-aminophenyl)-1,3,4-oxadiazole compounds such as shown in US. Pat. No. 3,189,447, and compounds having a pyrozoline nucleus as illustrated by US. Pat. No. 3,180,729. Accordingly, the novel tetranuclear methine dyes of the present invention which are suitably employed as dyestuff sensitizers in electrophotographic systems, can be employed advantageously in any of the aforementioned or similar photoconductive materials employed in photoconductive insulating layers.

The photoconductive insulating layers in which the tetranuclear methine dyestuff sensitizers of the present invention are incorporated are generally prepared as dispersions of the photoconductive material and dyestuff sensitizer in a solvent with the resultant dispersion applied to a suitable support, e.g. paper, alluminum plate, plastic, etc. In some instances, the photoconductive substances which are sensitized in accordance with the present invention by the employment of the novel tetranuclear methine dyes are used in the electrophotographic product and process in association with clear resinous polymeric binders having high dielectric characteristics. Such materials include, for example, polystyrene, polyvinylchloride, polyvinylacetate, polyvinylidenechloride, polyvinylacetals, polyvinylethers, polyacrylic esters, or any other natural or synthetic polymeric substance having the proper electrical characteristics. Thus, in the preparation of the photoconductive insulating layer employing the photoconductive material and sensitizing dyestuff of the present invention in association with such a clear, resinous polymeric binder, such materials are generally dissolved together in an organic solvent such as benzene, toluene, methylethylketone, methylethylbutylketone, chloroform,

methylenechloride, etc. Such solvent solutions are coated on a suitable carrier or support as noted above, and when the solution is dried by evaporation of the solvent material, a solid solution which is transparent is formed.

As noted previously, the support or carrier for the photoconducted insulating layer may be any material suitably employed in electrophotographic processes. Thus, for example, such support may include alluminum or other metal plates or foils; glass plates; paper sheets or webs; or plastic foils, especially foils made of electrically conductive resins. If paper is to be used as a support for the photoconductive layer, it is preferably that it shall have been treated against penetration by the photoconductive insulating coating solution, e. g. by treatment with methylcellulose in aqueous solution, polyvinyl alcohol in aqueous solution, etc. Of course, all of such support and carrier layers as well as the method of treating the same, and all of the photoconductive insulating materials discussed above are well known in the art of electrophotographic processes. In this respect, the present invention comprises an improvement in such electrophotographic processes and materials by providing a novel dyestuff sensitizer employed within the photoconductive insulating layer in an amount offrom about 0.01 percent to about 5 percent by weight, and preferably from about 1 percent to about 3 percent by weight based on the weight of the photoconductive insulating material.

In this respect, although the photoconductive insulating layer when charged in accordance with the electrophotographic process is slightly sensitive to light in the visible spectrum, it has been found generally necessary to extend the spectral sensitivity of such photoconductive materials into the visible part of the spectrum by the addition of a dyestuff sensitizer. Conventionally, such dyestuff sensitizers which have been found applicable are the triarylmethane dyes, xanthene dyes, thiazine dyes, acridine dyes, quinoline dyes, quinone dyes, anthraquinone dyes and cyanine dyes. The use of the novel tetranuclear methine dyes of the present invention within the photoconductive insulating layer as a dyestuff sensitizer in the electrophotographic process, however, has provided a distinct improvement over the use of such conventionally employed sensitizing materials in that, in addition to being capable of extending the spectral sensitivity of the photoconductive material by at least 50 percent, the dyestuff sensitizers employed in accordance with the present invention do not have associated with them the effect of producing fading or bleaching of the background of the photographic reproduction which effect is generally associated with previously employed materials.

In addition to the utility of the novel tetranuclear methine dyes of the present invention as dyestuff sensitizers in electrophotographic systems, the novel compounds of the present invention can also be utilized as sensitizers in conventional silver halide and similar photographic emulsions. Here again, the novel tetranuclear methine dyes are utilized for controlling or modifying the spectral sensitivity of the photographic emulsions. In this way, the novel compounds of the present invention are utilized for extending the spectral sensitivity of photographic silver halide emulsions, the natural sensitivity of light of which is restricted to a short range of wave lengths in the ultraviolet and/or sitizers for color photographic emulsions and X-ray violet and/or blue regions of the spectrum, to light of emulsions employed in X-ray photography. In addition, other wave lengths or to enhance the natural sensitivity the dyestuff sensitizers of the present invention need in the well-defined part of the spectrum, e.g. in the blue not be employed alone in the photographic silver halide range. 5 emulsion, but can be employed in conjunction with For optically sensitizing photographic silver halide other conventional sensitizing agents so as to produce a emulsions by using one or more of thetetranuclear super-sensitizing effect. methine dyes of the present invention, the dye or dyes The present invention will now be illustrated by can be incorporated in the photographic emulsion by reference to the following specific examples. It is to be one of the methods customarily p y in the 2111- m understood, however, that such examples are presented Thus, for ple it is Sometimee oohvehient to add for purposes of illustration only and the present inventhe dyestuff sensitizer to the emulsion in the form of a i i i no way to be deemed as limited theretu solution of the same in an appropriate solvent. The sensitizers are advantageously incorporated in the 15 EXAMPLEI finished, washed emulsions and should be uniformly distributed throughout such emulsions. The concentra- 33 fii ig 3 2 g i ffg tion of the dyestuff sensitizers in the silver halide emult x 1? ff g y foxysion can vary widely, for example, from about 0.001 me y mm me an y ms percent to about 5 percent by weight of the total emul- 2O sion composition. Preferably, however, the amount of O tetranuclear methine dye in the photographic silver ha- OH3S- N N 3 lide emulsion will vary from about 0.1 percent to 3 per- 01H 01H,

cent by weight, although greater or lesser amounts can be advantageously employed according to the effect 650 moles) of the complex Salt of '6- desired ethylrhodanine-methine cyanine] are pre-heated with In addition, the tetranuclear methine dyes f the ml. of purified chlorobenzene in a constant tempresent invention may, if desired, also be added to the perature bath (131C.) for 10 minutes with occasional emulsion by the well known expedient of bathing the stirring. After the addition of 30 ml. of freshly purified coated emulsion in asolution of the sensitizer. 30 dimethyl lf t the mixture was heated f an ddi- In PFePariPg the photographic emulsions q i s tional five minutes only. After it cooled, the reaction to the o the usual addefnda Such as anufoggmg mixture was triturated three times with ethyl ether and agents stablhzers ann'bronzmg agents hardeners the solid after standing overnight was filtered. The yield wetting agents, plasticizers, development accelerators, was quantitative as a dark brown 801i d without any color couplers, fluorescent brighteners and ultraviolet rification screening compounds can moreover by incorporated in the emulsion in the manner customarily employed in EXAMPLE [I the art.

Emulsions sensitized with the novel tetranuclear dyes The Preparahoh of tetrahholeef oy can be coated in the usual manner on a suitable support 40 y y Y' y y such as glass, cellulose derivative film, resin film or 2-(3-carboxyethyl-6-methoxy-2-benzothiazolinypaper. lidene)methyl-3-ethyl-4-oxo-5-thiazoliny- While the dyestuff sensitizers of the present invenlidene]methylene-3-ethyl-4-hydroxide thiazolinium tion are generally incorporated in silver halide emulhydroxide inner salt N C2115 N izHigQrH 121140 02H sions containing gelatin as a binding agent so as to ex- 0.18 g. (0.5 mrnole) of the quaternary salt of Examtend the spectral sensitivity thereof, such tetranuclear l 1, (136 (0,95 le) of 3-carb0xyethyl-6- methine y can also be Included In other P methoxy-2-methylbenzothiazolium iodide and 5 ml. of

graphic emlflsiohs sufih for i gelatin) Silver isopropanol were mixed thoroughly before the addition chlorobromide, gelatino silver bromide, gelatino silver of Q4 mL of triethylamina The mixture was Stirred gg g? and lgilatmo chlorotbromolodlgf' manually for two minutes and heated on a steam bath Otograp 1c emu sions con ammg wa er'permea e for three minutes with stirring after it boiled. The reaccolloids other than gelatin, such as agar-agar, zein, collodion,water-soluble cellulose derivatives, polyvinyl alnon mlxture was then dluted wuh three volumes of cohol or other hydrophilic synthetic or natural resins or water neutmhzed wlth glaclal P F (10 percent polymeric compounds, may equally well be sensitized eXFeSS) and whole was Chlued lcewat er for 20 according to the present invention, minutes. After it was filtered, the dye was boiled three In addition to optically sensitizing and extending the times with methanolsome 020 gp y spectral sensitivity of black and white photographic of photographic grade of titled dye was obtained as a emulsions, the novel tetranuclear methine dyes of the greenish powder melting at 220-224C with decompresent invention are similarly useful as dyestuff senposition.

EXAMPLE III EXAMPLE IV The preparation of the tetranuclear dye: 2-( 3-carboxyethyl-6-methoxy-2-benzothiazolinyidene)methyl-S-[ 2-(3-carboxyethyl-6-methoxy-Z- benzothiazolinyidene)methyl-3-ethyl-4-oxo-5- thiazolinyidene]methylene-3-carboxyethyl-4-hydroxide thiazolinium hydroxide inner salt.

The above tetranuclear dye was prepared by following the procedure of Example II with the exception that the quaternary salt of Example I was replaced by an equal amount of the salt -(3-ethyl-2-methylthio-4- oxo-5-thiazolinylidene)methyl-3-carboxyethyl-4- hydroxy-Z-methylthiothiazoline anhydro salt. A substantially equivalent yield of the photographic grade dye was produced.

EXAMPLE V A dyestuff of the formula:

L Ouc was prepared by following the procedure of Example II, except that the 3-carboxyethyl-6-methoxy-2-methylbenzothiazolium iodide was replaced with an equivalent amount of 3-carboxyethylrhodanine. Again, a substantially equivalent yield of the tetranuclear dye of photographic grade was prepared.

l8 EXAMPLE VI Example V was repeated except that 3-carboxymethylrhodanine was employed in lieu of 3-carboxyethylrhodanine. Again, a substantially equivalent yield of the photographic grade tetranuclear dye was produced.

EXAMPLE VII Example V was again repeated except that an equivalent amount of 3-ethylrhodanine was employed in lieu of 3-carboxyethylrhodanine. Again, a substantially equivalent yield of the desired tetranuclear dye was produced.

EXAMPLE VIII Example V was repeated except that 5-(3-ethyl-2 methylthio-4-oxo-5-thiazolinylidene)methyl-3-ethyl-4- hydroxy:2-methylothiothiazoline anhydro salt was replaced with a substantially equivalent amount of 5- (3-ethyl-2-methylthio-4-oxo-5-thiazolinylidene)methyl-3-carboxyethyl-4-hydroxy-2- 5 methylthiothiazoline anhydro salt. A substantially equivalent yield of the desired tetranuclear dye of photographic grade was produced.

OCH:

EXAMPLE IX Example VII was repeated except that 5-(3-ethyl-2- methylthio-4-oxo-5-thiazolinylidene)methyl-3-ethyl-4- hydroxy-2-methylthiothiazoline anhydro salt was replaced with a substantially equivalent amount of 5- (3-ethyl-2-methylthio-4-oxo-5-thiaz0linylidene)methyl-3-carboxyethyl-4-hydroxy-2- methylthiothiazoline anhydro salt. The desired tetranuclear dye was produced in substantially equivalent yield as produced in the examples above.

EXAMPLE X The preparation of 5-(3-ethyl-2,4-dione-5-thiazolinylidene)-methyl-2-[2-(3-carboxyethyl-6-methoxy-2- benzothiazolinylidene)-methyl-3-ethyl-4-oxo-5- thiazolinylidene]-3-ethyl-4-hydroxide-thiazolinium hydroxide inner salt.

N S /S\ OCH: 1 e C2115 C2H5 0 '-=CHC I 2H5 I? CrHlCOzH 0.25 g. (0.56 mmole) of 2-(3-ethyl-4-oxo-2-thio-5- thiazolinylidene)-5-( 3-ethyl-2 ,4-dione-5-thiazolinylidene) methylene-3-ethyl-4-hydroxide-thiazolinium hydroxide inner salt was preheated with 2 ml. of chlorobenzene in a constant temperature (131C) with the subsequent addition of 2 ml. of dimethyl sulfate. The mixture was then heated for 5 mins. After it cooled, the reaction mixture was triturated three times with ethyl ether. This was reacted directly without purification with 0.16 g. (0.42 mmole) of 3-carboxyethyl- 6-methoxy-2-methylbenzo-thiazolium iodide in 5 ml. of isopropanol and 0.4 ml. of triethylamine. The mixture was heated on a steam bath with stirring for three minutes. The reaction mixture was treated in the same manner as described in Example II. A yield of 0.12 g. (32.3 percent yield) of the unsymmetrical tetranuclear dye melting at 27780C with decomposition was obtained.

EXAMPLE XI The procedure of Example X was repeated except that the 3-carboxyethyl-6-methoxy-2-methylbenzothiazolium iodine was replaced with an equivalent amount of the following compounds:

A. 3-carboxyethyl-2-methylbenzothiazolium iodide B. 3-carboxyethyl-6-methoxy-2-methylbenzoselenazolium iodide C. 3-carboxyethyl-Z-methylbenzoselenazolium iodide D. 3-carboxybutyl-6-methoxy-2-methylbenzothiazolium iodide.

Here again, substantially equivalent yield of photographic grade tetranuclear dyes of the unsymmetrical type were prepared.

EXAMPLE XII The following experiment was conducted in order to illustrate the sensitizing property of the novel tetranuclear dyes when employed in electrophotographic systems.

A solution was prepared by admixing with stirring 260 ml. of toluene, 0.09 g. of colbalt naphthanate and 0.09 g. of manganese naphthanate. After the formation of a clear solution, 91 g. of an electrostatic coating, i.e. Epitex l3ll (Celenese Corporation) comprising a mixture of a polyester of bisphenol-A-polyglycidyl ether, soya fatty acids, and dimeric linseed fatty acids was added with stirring. In addition, 18.2 g. of a low molecular weight (approximately 400), low melting point (approximately 75C) polystyrene resin were added to the system. Subsequently, 454 g. of zinc oxide were added to the system with stirring and milling until a smooth homogeneous composition was prepared.

To such a smooth, homogeneous, milled composition mg. of the sensitizing dyes of Examples 11, Ill(a), V, VI, VII and IX dissolved in methanol were added. The compositions including the sensitizing tetranuclear dyes of the present invention were then stirred for 30 minutes to provide a homogeneous distribution of the sensitizing dye in the conductive coating and such homogeneous composition was then coated on Weyerhaeuser Copybase G conductive paper with drying to a dried coating weight of 20 pounds per 3,000 square feet.

The conductive paper thus coated with a conductive coating including the sensitizing tetranuclear dyes of the present invention were then evaluated by means of spectrograms with the prints being evaluated in a Bruning Copytron 2000. The prints and spectrograms were then compared to those prepared from an unsensitized coating, such comparison indicating a sensitization in the long wave length region, i.e. red region, of at least 50 percent. This, therefore, establishes the utility of the tetranuclear dyes of the present invention as optical dyestuff sensitizers in electrophotographic processes.

In a comparison with conventional dyestuif sensitizers generally employed in electrophotographic processes, compositions were prepared as above except utilizing dyestuff sensitizers Bromphenol Blue, Fluorescin, Eosin, Rose Bengal and carbocyanine dyes. While the above conventional dyestuff sensitizers did have the effect of sensitizing or extending the spectral sensitivity of the photoconductive material, such dyestuff sensitizers provided a fading or bleaching of the background image. Such fading or bleaching of the background image upon long exposure to light was far less pronounced when employing the dyestuff sensitizers of the present invention.

Accordingly, it should be clear from the above that the novel tetranuclear dyes of the present invention have found exceptional utility as dyestuff sensitizers, particularly in electrophotographic processes wherein such dyestuff sensitizer is incorporated within a supported conductive layer. In this respect, the dyestuff sensitizers of the present invention have been found capable of providing an unexpectedly great sensitization of the spectral sensitivity of the conductive material employed in the electrophotographic processes while eliminating the deficiencies associated with the effect of fading or bleaching of the background image.

Thus, while the present invention has been described primarily with respect to the foregoing specific examples, it should be understood that the present invention is in no way to be deemed as limited thereto but should be construed as broadly as all or any equivalents thereof.

I claim 1. Novel tetranuclear compound of the formula:

wherein A is selected from the group consisting of i'T s o i.

and

B is selected from the group consisting of (1),

R, is selected from the group consisting of hydrogen lower alkyl and lower alkoxy; and

Y is selected from the group consisting of Se and S; Q 4. The compound of claim 1 wherein said compound such compounds being characterized that when A corresponds to the formula: is(l),l3is(1);andwhenAis(2),Bis(3). H

2. The compound of claim 1 wherein said compound 8 8 corresponds to the formula: 5 L 3 0 H s l s |I+ s (IJ s 6 S- O 0211 0- s O O- S N on on ('0 H Z J 2 J L N/ N 10 93112011200211 1 cmomoom s 0 431m I 0- s 5. The compound of claim 1 wherein said compound :11 (IIHZ CHEC 02H 5 (13112011200211 corresponds to the formula.

3. The compound of claim 1 wherein said compound corresponds to the formula: 15 -L=g-Hs H S 0 0-0 ii 5 H+ s ('3 S III/ \N L e s 0 01m 0 s 0 O- S N \N/ bu N/ \N/ H+ CH2CH2C 02H l L 2H5 CzHs S 0 21 5 I O\ s f Cam N 6. The compound of claim 1 wherein said compound CHzC 0211 5320 211 I corresponds to the formula:

CHzCHzC 02H UNITED STATES PATENT OFFICE CERTIFICATE 0F CORREQTION Patent No. 3 3 Dated August 29, 1972 Inventofls) Shi-Kuang Yao It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, for the first formula at the top of the second column, read:

Column 1, lines 52-55, for the formula opposite these lines,

FORM P0405) uscoMM-oc 6O376-P69 U.S. GOVERNMENT PRINTING OFFICE i 19.9 0568-334,

Patent No. 3,687,946 P 2 Column 3, lines 30 et seq., for the formula opposite these lines, read:

. H s CH- ,s- Y

r e 'R C-CH 0 0-0. CH- R N C 3 N I N R R R2 2 Columns 5 and 6, for the seco nd formula from the top, read:

OC H H H CZO Se s CH V f 2p-cn l llq;o e 0-T;=CH-C\ I ,N C2'H5 C2H5 T (301mm 9 and 10, for the fifth and sixth formulas from the c ztead:

5 H 2 N C H w 2 O C A H 2 0 5 H 2 C E 5 H 2 N C in!!! s S U S H 2 s "M 2 N c s 9 H A. C 0 3 H9 N -Q Sl.|| a w Patent No. 3,687,946 page 4 Column 16, lines 19-23, for the formula opposite these lines,

Claim 1, lines 40-45, for the formula opposite these lines, read:

A; ;O 6 H+ V N o-c N B Signed and sealed this 25th day of March 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks 

2. The compound of claim 1 wherein said compound corresponds to the formula:
 3. The compound of claim 1 wherein said compound corresponds to the formula:
 4. The compound of claim 1 wherein said compound corresponds to the formula:
 5. The compound of claim 1 wherein said compound corresponds to the formula:
 6. The compound of claim 1 wherein said compound corresponds to the formula: 